Manufacture of rubber articles



Patented Sept. 10, 1935 I UNITED STATES PATENT OFFICE MANUFACTURE OF RUBBER ARTICLE Walter Kay, Bury, England, assignor to Kaysam Corporation of America, Dover, DeL, a corporation of Delaware No Drawing. Application November 1, 1932, Serial No. 640,650. In Great Britain November 5, 1 31 8 Claims. (01. 18-58) This invention relates to rubber or rubber-like natural or preserved or vulcanized or even precompositions and to articles manufactured thereagglomerated, or an aqueous dispersion of crude from. The invention is particularly applicable or vulcanized rubber (either reclaimed or virgin), to the manufacture of such articles as rubber an aqueous dispersion manufactured by chemical soles and heels, rubber bathing shoes, rubber synthesis from such substances as isoprene, boots and shoes of all kinds and rubber balls, butadiene or their homologues, and other like rubber flooring such as tiles and mats and motor dispersions.

car running boards, and in fact, to molded rubber The quicker the actual setting, the better the goods in general, hollow or not. results, and it is one great advantage of the proc- One object of the invention is to provide an ess according to the invention that a very quick improved method of forming a sensitive mix consetting agent, or a relatively large quantity of taining rubber latex capable of setting or gelling a setting agent, may be used without risk of without synzeresis. Another object is to provide premature setting. The better results of quick means for controlling the time of setting or gellsetting are due to two causes; on the one hand mg of such a mix, Yet another object is to proslow setting leads to the formation of a coarse 15 vide a method whereby articles having parts difand soft product, and on the other hand there is fering widely in thickness may be manufactured some tendency for the powders in the mixture to from a sensitive latex mix. settle out, so that the product is less homogene- In proceeding in accordance with the present ous if the setting is slow. Furthermore, speed in m invention a stable mix is formed from an aqueous setting means that the formed bodies can be redispersion of natural or synthetic rubber with moved from the molds quickly and thus the or without one or more fillers, vulcanizing agents amount of apparatus for a given output can be or other ingredients, and with or without added reduced. It is, therefore, desirable either to water, preferably in such a way that the mix use a very quick setting agent or to use a relahas a total dry residue content of more than tively high proportion of the setting agent. In 25 60%. This mix is then rendered unstable by the conjunction with this it is desirable to use a addition of a setting agent. It is to be underhighly concentr d sp vin a dry stood that the initial mix is stable in that'it can residue content of about 70% 1' more. 101 101' be kept under the same conditions as the disperexample asthe concentrated rubber latex sold sion itself without coagulation or setting taking under the registered trade mark Revertex. As place, that is to say it can be kept at any ordiis well known Revertex differs from other nary temperature for an almost indefinite period. latices in that the preservative by which it is kept When, however, the setting agent is added, the unchanged is a non-volatile alkali and not amresultant mixture promptly becomes unstable, monia and that it contains all the non-rubber that is to say, it can no longerbe kept indefinitely, erum solids originally present in the natural 5 but if poured into an open shallow mold, for exlatex.- In such a highly concentrated dispersion ample, it will set, completely and irreversibly in e ubber par icles are very c ose together and,

a longer or shorter time according to its compositherefore, when the setting is quick a very good tion and the temperature. An important feature tough product is obtained. The use of a highly or the invention consists, therefore, in pouring c n entr d latex also affords the great advanthe resultant mixture into a mold immediately or i ge that, prior t the p of being worked into almost immediately after the addition of the setthe latex, the va s e i nts can be dissolved ting agent. If desired, the mold may then be or suspended in adequate quantities of water for heated to cause the mixture to set. The mixthe mixing to take place easily without the pro- 5 ture y b kept for few minutes before it is portion of the dry residue to the whole being re- 5 poured to t e d b at the ordinary duced to such an extent that the final rubber perature of the work-room in which the'heating product when set would not be sumciently of the mold? is takmg the g e k form for practical purposes. 0n the other hand,

mg setimg the lmxlfure beg'ms stralght it has been found that with the use, for example,

go way and general the mixture should 1101? be of an unconcentrated latex or a latex of lower ID k p 1 m than ten minutes before i is D m concentration, the added ingredients have either into the molds. to be added dry or wetted with relatively small The term "aqueous dispersion of natural or quantities of water, in which case there is a consynthetic rubber is intended to include rubber siderable tendency for coagulation to take place 6 latex, whether concentrated or not and either at least locally. or they must be added in such and the resultant mixture is poured into a mold. In order to obtain the quick setting which is so desirable, the moldshould be heated to, for example, 80 to 90 C. If, however, cold setting is desired, the proportion of the setting agent should be increased, for example, by taking 380 cc. of a 71% ammonium nitrate solution.

Another example is as follows: A mix is made consisting of:

Grams.

Rever x 1300 Lithopone- 300 (Wetted out with 300 cc. of water.)

Sulphur- 30 Zinc diethyl dithiocarbamate l Magnesium oxide 50 (Wetted out with 250 grs. of 2/n trisodiumphosphate.) I

This mix is rendered highly unstable by adding to every 100 grs. of the mix 10 cc. of a 10% solution of ammonium chloride. This'mixture sets in the cold in a short time.

In certain cases, where a sufilciently concentrated dispersion is used, the setting agent may said washers become embedded in the set mixture.

2. The process of manufacturing an article which comprises the following steps: forming a stable mix from an aqueous dispersion of natural or synthetic rubber containing a non-volatile alkali, rendering the mix unstable and decreasing the viscosity thereof by the addition of a setting agent, pouring exactly the required quantity of the resultant mixture into a mold, said mixture setting without synicresis to form an irreversible gel, removing the set article from the mold, and washing and dryin the removed article while permitting the escape of water therefrom.

3. The process of manufacturing an article which comprises the following steps: forming a stable mix from an aqueous dispersion of natural or synthetic rubber containing non-volatile alkali, the rubber particles thereof being normally negatively charged, adding to the mix a setting agent which will -bring about a change to positive in the charge of the rubber particles in the resultant mixture, and pouring exactly the required quantity of such mixture into a mold, said mixture setting without syncresis to form an irreversible gel.

' required quantity of such mixture into a mold,

4. The process of manufacturing an articlev which comprises the following steps: forming a stable mix from an aqueous dispersion of natural or synthetic rubber containing non-volatile alkali, the rubber particles thereof being normal-. 5

1y negatively charged, adding to the mix a setting agent which will bring about a change to positive in the charge of the rubber particles in the resultant mixture, and pouring exactly the said mixture setting without synaaresis to form an irreversible gel, removing the set article from the mold and washing and drying the removed article while permitting the escape of water therefrom.

5. The process of manufacturing an article which comprises the following steps: forming a stable mix from a concentrated aqueous dispersion of natural or synthetic rubber having a total dry residue content of more than- 60%, a nonvolatile alkali, and a metallic oxide, hydroxide or salt, and adding thereto a setting agent being or containing an ammonium salt which renders the mix unstable, the metallic oxide, hydroxide or salt in the presence of the setting agent acting upon the non-volatile alkali in the dispersion to form free ammonia, thereby decreasing the viscosity of the mixture, and setting bodies which, as'the ammonia evaporates, set the mixture without synaeresis to form an irreversible gel.

6-. In a process of making an article of rubber, the steps comprising mixing with concentrated,- or thickened aqueous dispersion of rubber an ammonium salt providing sufllcient positively charged ions to cause irreversible setting of the mix without synaeresis, said salt being of the group consisting of chloride, nitrate, carbonate,

and acetate, casting the mix to a desired form, and maintaining the mix in such form until it has set to a stable condition.

7. In a process of making an article of rubber, the steps comprising mixing with an alkaline aqueous dispersion of rubber containing a vulcanizing agent and'a zinc compound an ammonium salt providing sufficient positively charged ions to cause irreversible setting of the mix without synmresis, said salt being of the group consisting of chloride, nitrate, carbonate, and acetate, casting the mix to the desired form, maintaining the mix in such form until setting to a stable condition has taken place, washing and drying the cast article, and subsequently vulcanizing the same.

8. Process of making an article of rubbe which comprises casting to the desired form a mixture containing an alkaline aqueous dispersion of rubber, a vulcanizing agent, zinc compound, and ammonium nitrate in an amount suillcient to cause irreversible setting without synairesis, maintaining the shape of the mixture until such setting an has occurred, washing and drying the article, and subsequently vulcanizing the same.

wan'rna KAY. 

